1. Field of the Invention
The present invention relates to apparatus and method of performing heat treatment on a workpiece substrate, e.g., a semiconductor wafer, an LCD glass substrate or the like that has been coated and developed, and to a recording medium recording a program for practicing the method.
2. Description of the Background Art
Generally, in manufacturing a semiconductor device, the photolithography technique is used for forming a thin film of ITO (Indium Tin Oxide) or an electrode pattern on a semiconductor wafer, an LCD glass substrate or the like (hereinafter referred to as a wafer or the like). In the photolithography technique, photoresist is coated on a wafer or the like to form a resist film. The formed resist film is exposed in accordance with a prescribed circuit pattern. By developing the exposed pattern, the circuit pattern is formed on the resist film.
In such a photolithography process, various types of baking processing are performed, such as baking processing after resist coating (pre-bake), baking processing after exposure (post-exposure bake), and baking processing after developing processing (post-bake).
One known conventional heat treatment apparatus performing such processing is configured for forming a heat processing atmosphere by a heat plate having a heater embedded and a cover body covering the heat plate. The heat treatment apparatus performs heat treatment on the wafers or the like placed on the heat plate by setting the processing atmosphere to a processing temperature by the radiant heat from the heat plate. Here, unlike the heat plate, the cover body forming the processing atmosphere does not have its temperature controlled. Therefore, even during the heat treatment, the temperature of the cover body remains lower than the set temperature of the heat plate, affecting the processing temperature and resulting in unstable heat treatment. Accordingly, there is a known conventional heat treatment apparatus having a structure in which a heat pipe is embedded in the cover body so as to improve the heat transfer performance of the cover body (e.g., see Japanese Patent Laying-Open No. 2000-183069).
Meanwhile, generally in the photolithography process, wafers or the like on a lot-by-lot basis are continuously carried to (carried into) processing portions including a heat treatment apparatus and processed. The processed wafers or the like are carried away from the processing portion, and thereafter wafers or the like of the subsequent lot are similarly processed. Accordingly, the heat treatment apparatus is in a standby mode in a period after processing of the wafers or the like of the preceding lot is finished and until processing of the wafers or the like of the subsequent lot is started. The temperature of the treatment chamber in this period varies depending on whether the cover body is open or closed. When the cover body is closed as the normal state, the temperature in the treatment chamber is higher than the processing temperature. Conversely, when the cover body is open, the temperature in the treatment chamber is lower than the processing temperature. Accordingly, there has been a problem that the processing temperature for the wafers or the like of the subsequent lot carried into the heat treatment apparatus becomes unstable, resulting in an uneven processing accuracy such as an uneven line width in the baking processing after exposure, and a reduction in yield.
A possible solution to such a problem may be to adjust the heating temperature of the heat plate to maintain the processing temperature. However, as described above, since the temperature of the treatment chamber is affected by the temperature of the cover body and becomes lower than the temperature of the heat plate, it is difficult to maintain the processing temperature by adjusting the heating temperature of the heat plate. As to the apparatus disclosed in Japanese Patent Laying-Open No. 2000-183069, while it shows excellent responsiveness to the change in the temperature of the treatment chamber associated with increase or decrease in the temperature of the heat plate owing to the enhanced heat transfer performance, it is still difficult to maintain the processing temperature by adjusting the heating temperature of the heat plate and cover body. Moreover, the apparatus disclosed in Japanese Patent Laying-Open No. 2000-183069 additionally suffers from a complicated structure and an increased size.